Improve the diagnostics in udf compiler for try-and-catch. (#3668)

Signed-off-by: Sean Lee <selee@nvidia.com>

docs/additional-functionality/udf-to-catalyst-expressions.md

@@ -110,3 +110,5 @@ When translating UDFs to Catalyst expressions, the supported UDF functions are l
 |                          | lhs :+ rhs                                               |
 | Method call              | Only if the method being called 1. Consists of operations supported by the UDF compiler, and 2. is one of the folllowing: a final method, a method in a final class, or a method in a final object |
 
+All other expressions, including but not limited to `try` and `catch`, are unsupported and UDFs
+with such expressions cannot be compiled.

udf-compiler/src/main/scala/com/nvidia/spark/udf/LambdaReflection.scala

@@ -92,6 +92,10 @@ class LambdaReflection private(private val classPool: ClassPool,
 
   private val codeAttribute = methodInfo.getCodeAttribute
 
+  if (codeAttribute.getExceptionTable.size > 0) {
+    throw new SparkException("exception handling (try-and-catch) isn't supported")
+  }
+
   lazy val codeIterator: CodeIterator = codeAttribute.iterator
 
   lazy val parameters: Array[CtClass] = ctMethod.getParameterTypes

udf-compiler/src/test/scala/com/nvidia/spark/OpcodeSuite.scala

@@ -890,6 +890,24 @@ class OpcodeSuite extends FunSuite {
     checkEquivNotCompiled(result, ref)
   }
 
+  test("FALLBACK TO CPU: exception handling - unsupported") {
+    val myudf1: Int => Int = { a =>
+      var x:Int = 0
+      try {
+        x = a
+      } catch {
+        case ex: Exception => { }
+      }
+      x
+    }
+
+    val u1 = makeUdf(myudf1)
+    val dataset = List(1, 5, 3, 7).toDS()
+    val result = dataset.withColumn("new", u1('value))
+    val ref = dataset.withColumn("new", col("value"))
+    checkEquivNotCompiled(result, ref)
+  }
+
   test("conditional doubles test2") {
     val myudf: Double => Double = { x =>
       val t =